In the subtractive color photography system used normally in the field of photographic technology for obtaining color images, aromatic primary amine type color developing agent, hereunder, it is simply called color developing agent, is used for developing silver halide grains after image-wise exposure, as is known very well. Through a reaction between the oxidized product of the color developing agent generated by the development of the silver halide grain and a coupler of a certain type, yellow, magenta or cyan dye images can be formed.
The dye images thus obtained are required not to change and fade colors even when they are exposed to light for a long time or preserved under the condition of high temperature and high humidity. However, the lightfastness of actual dye images to ultra-violet rays or visible light is not satisfactory, besides, preservability in dark place is not sufficient. Therefore, the improvement of image preservability under various conditions has been an endless theme in the research and development field.
With regard to the improvement of such image preservability, various studies such as the improvement of the image preservability of dye formed from coupler itself and the development of image stabilizer have been made.
Among them, conventional phenol type cyan coupler having an alkyl group at its fifth position which are used widely as a cyan coupler, have a certain level of lightfastness, but it is not satisfactory. Moreover, such type cyan couplers have a problem that they are considerably poor in dark preservability. As a cyan coupler which has improved in its dark preservability, 2,5-diacylaminophenol type cyan coupler is known, for example, it is disclosed in U.S. Pat. No. 2,895,826, Japanese Patent Publication Open to Public Inspection, hereinafter referred to as Japanese Patent O.P.I. Publication, Nos. 112038/1975, 109630/1978 and 163537/1980. However, the lightfastness of the dye image obtained from 2,5-diacylaminophenol type cyan coupler has been deteriorated in many cases, though the dark preservability thereof has been improved remarkably.
In order to solve such problems, methods in which the above-mentioned two couplers are used in combination are disclosed in many patent publication including Japanese Patent O.P.I. Publication No. 100440/1984. However, it has naturally been difficult to cover the weak points of each coupler. Therefore, further basic improvement has been necessary for the couplers.
On the other hand, various attempts have been made to cause both image stabilizer and cyan coupler to exist together and thereby to improve the image preservability. Methods to use U V absorbing agent and various stabilizers are disclosed in Japanese Patent Examined Publication Nos. 31256/1973 and 31625/1973, U.S. Pat. Nos.3,069,262, 3,432,300 and 3,574,627 and Japanese Patent O.P.I. Publication Nos. 221844/1983, 124340/1984, 232649/1987 and 178258/1987, but, all of them are insufficient in terms of their effect.
Recently, there have been studied the methods to improve image preservability by using specific materials as media as for dispersing the coupler. For example, they have been opened in Japanese Patent O.P.I. Publication Nos. 129853/1987, 178259/1987, 44658/1988 and 250648/1988 and No. 20545/1987. In many cases, however, color forming efficiency is deteriorated remarkably. With regard to image preservability, lightfastness or dark preservability is improved but other factors are not improved or deteriorated remarkably.
The image preservability of magenta dye image wherein the color balance in time of fading was rate-determined has been increased by the development of various anti-fading agent recently. Therefore, in order to maintain the color balance in time of fading, it has become necessary to further improve the preservability of cyan dye image.